Desalination is being increasingly practiced to produce freshwater from saltwater. The most commonly practiced desalination processes are reverse osmosis (“RO”), nanofiltration (“NF”), thermal desalination, and electrodialysis (“ED”) or electrodialysis reversal (“EDR”). In RO, water is forced through a membrane that rejects salts and allows water flux under pressures exceeding the osmotic pressure. NF is similar to RO, although NF produces a permeate richer in salts of monovalent ions than RO permeate. In thermal desalination, water is evaporated and then condensed, sometimes in multiple stages, in order to recycle the latent heat of condensation.
ED and EDR are water treatment processes that transfer salt ions across ion exchange membranes under the action of a galvanic potential. Conventional ED is typically performed using an electrodialysis stack comprising alternating anion exchange membranes and cation exchange membranes between two electrodes (an anode and a cathode). The galvanic potential is supplied as a voltage generated at the electrodes. Typical industrial ED stacks comprise two sets of chambers: product chambers and concentrate chambers. One water source is typically used to feed a product circuit and a concentrate circuit, which respectively comprise the product chambers and the concentrate chambers. During stack operation salts are transferred from the product to the concentrate chambers. Desalinated product water is recovered and the concentrate is eventually discharged as a waste.